Waterborne diseases due to microbial contamination in drinking water are the major health problems throughout the world and providing safe drinking water to the common man is emerging as one of the major challenges of this century. Water purification systems using membrane processes like reverse osmosis, nanofiltration, ultrafiltration, electrodialysis for filtering and purifying water to obtain safe potable water are available in the market. Among these membrane processes, ultrafiltration process is the most efficient process in terms of productivity because of its high water permeability particularly in the treatment of impure turbid water containing suspended particles, pathogens and other harmful microorganisms. Different membrane types of water ultrafiltration process exist in the market, one of which is based on polymer hollow-fiber.
References may be made to patent JP 2006088148, wherein a process for making a polysulfone ultrafiltration hollow fiber membrane used for water treatment is disclosed. The hollow fiber has sponge structure having 10-220 micron pore size in the inner surface and 0.01-5 microns pore size on the outer surface.
References may be made to patent EP927572-A, wherein a process for making hollow fiber membranes from a spinning dope comprising of polysulfone, polyvinylpyrollidone and organic solvent using mixture of inorganic salt, diethylene glycol and water as internal bore forming liquid and water or water with DEG/CaCl2 as external coagulating liquid has been disclosed. These fibers are having pore size suitable for the separation of cytochrome-C having molecular weight of 12400 g/mol.
References may be made to patent US2004026315-A1, discloses a process for making polysulfone hollow fine fiber membrane from a mixture of polysulfone, a hydrophilic polyvinylpyrrolidone and solvent using melt spinning process having fiber diameter of about 200 micron for application in dialysis.
References may be made to patents CN1557532-A; CN1261197-C, wherein a process of polysulfone fiber making from a mixture of polysulfone and polyvinylpyrollidone through dry and wet spinning process resulting to fiber having 0.7 to 2.0 mm inner diameter for using in city water processing has been disclosed.
References may be made to patent EP 0568045 A1, wherein polysulfone-PVP based hollow fiber membrane where the PVP content in inner skin layer is higher than the outer skin layer by extrusion at 50° C. having fiber diameter of 280 micron for application in body fluid treatment has been disclosed.
References may be made to patent JP 09052028, wherein spinning of polyacrylonitrile hollow fiber after degassing the spinning dope at above room temperature and purging with an inert gas for improving the spinning stability of the PAN fibers has been disclosed.
References may be made to Journal “Separation and Purification Technology 2006, 52(2), 380-387” wherein Yu, D-G et al. reported fabrication of polyacrylonitrile (PAN) hollow fiber membranes from PAN fibers spun via the dry-jet wet spinning process and have shown the influence of draw ratio to the fiber properties.
References may be made to Journal “Journal of Membrane Science 1997, 132(1), 63-71), wherein Yang, M.-C. and Tong, J. H. reported spinning of PAN hollow fiber and modification by surface hydrolysis forming a thin layer of polyacrylic acid on the surface of the hollow fiber having rejection of myoglobin and cytochrome-C having molecular weight of about 12000-16000 g/mol.
References may be made to patent CN 1110625, wherein flat-sheet membranes have been developed from the blend of polyacrylonitrile and polysulfone by solution casting and evaporation techniques.
The prior art have many drawbacks. For example, polysulfone fiber of the prior art is hydrophobic which may result in less flux and more fouling prone while in operation. The PAN fiber being hydrophilic and relatively more flexible with smooth surface is prone to shrinkage and brittleness in dry condition resulting to difficulties in handling and long-term storage.